Dpb11, which interacts with DNA polymerase II(epsilon) in Saccharomyces cerevisiae, has a dual role in S-phase progression and at a cell cycle checkpoint.

DPB11, a gene that suppresses mutations in two essential subunits of Saccharomyces cerevisiae DNA polymerase II(epsilon) encoded by POL2 and DPB2, was isolated on a multicopy plasmid. The nucleotide sequence of the DPB11 gene revealed an open reading frame predicting an 87-kDa protein. This protein is homologous to the Schizosaccharomyces pombe rad4+/cut5+ gene product that has a cell cycle checkpoint function. Disruption of DPB11 is lethal, indicating that DPB11 is essential for cell proliferation. In thermosensitive dpb11-1 mutant cells, S-phase progression is defective at the nonpermissive temperature, followed by cell division with unequal chromosomal segregation accompanied by loss of viability.dpb11-1 is synthetic lethal with any one of the dpb2-1, pol2-11, and pol2-18 mutations at all temperatures. Moreover, dpb11 cells are sensitive to hydroxyurea, methyl methanesulfonate, and UV irradiation. These results strongly suggest that Dpb11 is a part of the DNA polymerase II complex during chromosomal DNA replication and also acts in a checkpoint pathway during the S phase of the cell cycle to sense stalled DNA replication. IMAGES:

DPB11基因可抑制由POL2与DPB2编码的酿酒酵母（Saccharomyces cerevisiae）DNA聚合酶Ⅱ（ε）两个必需亚基的突变，该基因通过多拷贝质粒得以分离克隆。DPB11基因的核苷酸序列分析显示，其携带一个可编码87 kDa蛋白质的开放阅读框（open reading frame, ORF）。该蛋白质与具备细胞周期检验点功能的粟酒裂殖酵母（Schizosaccharomyces pombe）rad4+/cut5+基因编码产物同源。敲除DPB11会导致细胞死亡，这表明DPB11对细胞增殖必不可少。在温度敏感型dpb11-1突变体细胞中，非许可温度下S期进程存在缺陷，随后细胞会发生染色体分离不均的分裂，并伴随细胞活力丧失。在所有温度条件下，dpb11-1与dpb2-1、pol2-11及pol2-18中的任意一种突变均会表现出合成致死（synthetic lethal）效应。此外，dpb11突变体细胞对羟基脲（hydroxyurea）、甲基甲磺酸（methyl methanesulfonate）以及紫外线（UV）照射敏感。上述结果强烈表明，Dpb11在染色体DNA复制过程中是DNA聚合酶Ⅱ复合物的组成部分，同时也在细胞周期S期的检验点通路中发挥作用，以感知停滞的DNA复制进程。图片：